Thanks for bringing this issue up. You posted this in the Link development forum, so I guess you want to create some tools for link checking, the automation of link requests etc.
There is no such thing as the perfect programming language. It really depends on the type of work you want to do, the computer platform you are working on and which language you feel comfortable with.
That said, C is a language which can create extremely fast code, but you are working very close to the internals of the computer. If with SEO tools you mean programs which check links, rankings, etc then C might not be the right language.
PHP is on the other side of the spectrum. It is an easy scripting language with a syntax which is nor far from C or Java. If you know those two languages it is not difficult to grasp the fundamentals of PHP. PHP is easy to write, has a huge library with network type functionality but its drawback is that it is interpreted, hence a significant factor slower than C or Java. But for scripting to automate work and glue processes together it might be a good choice. PHP is especially a good language if you want your SEO tools to be web enabled. PHP seamlessly integrates with the Apache webserver and many websites are entirely written in this scripting language.
Python is in my feeling something in between. Still good for scripting but a little bit higher level. If my memory serves me well, Google is a happy user of python for many tasks.